1. Field of the Invention
The invention generally relates to distributed printing, wherein a plurality of printers concurrently process one print job in order to produce a requested number of copies of a document in a limited time interval. The invention also relates to a printing system in which the method according to the invention is implemented, and to computer software making a computer perform the method of the invention.
2. Discussion of Background Art
Distributed printing is for instance disclosed in U.S. Pat. No. 5,287,194, describing a system including a plurality of printers and a scheduler. In order to have a print job processed within a desired time interval, the print scheduler determines the job length and inspects the available printers. It selects the printer most suited for the job, and then checks if that printer can complete the job in time. If not, it selects another printer to take over the portion of the job the first printer cannot complete in time. In this way a job may be broken up in several portions each processed by another printer. U.S. Pat. No. 5,995,721 improves this scheduling method by giving an operator the opportunity to interfere with the scheduling process and reject certain printers that he does not want to process the print job, for instance, because such printers are too far away from his own location.
Generally, known distributed printing systems are centrally controlled by a scheduler that splits print jobs in portions and sends them to plural printers.
Another approach of quickly printing a number of copies of a print file involves concurrent printing in a so-called unchained interactive printing system as is disclosed in European Patent Application Publication No. EP 1 229 724 A2 owned by the present Assignee. In this particular form of printing, print files are submitted for printing, but never printed unless they are selected and started at the console of a printer by an operator. In a networked system comprising a plurality of printers, print jobs are made available for selection and subsequent printing at any of the connected printers. A print job remains selectable until it is specifically removed from the selection list, and can even be selected and started at one printer while it is being processed at another printer. In this way, several printers may be teamed up to print a large number of copies of the print file.
This solution differs from the methods described above in that the printing is not centrally controlled, i.e. the initiative to include a printer into the process is taken at the printer by an operator, and the print job is pulled from its source in the network by the printer instead of being pushed to the printers by the scheduler. An advantage of this approach is that printers may join the print process at different moments. If, for instance, a printer cannot handle the print job because of a remediable disablement, such as an empty print sheet tray or a paper jam, it may be restored to function and then be brought into the production process that is already running at other printers. This gives a great deal of flexibility.
A drawback of this approach, however, is that the operator, going from one printer to another, starting the same print job, must specify the number of copies to be made by each printer in order to arrive at the desired total number of copies. Also, when one of the printers suffers a malfunction during the processing, such as running out of print sheets, the desired number of copies will not be completed until the malfunction is remedied.